1. Field of the Invention
The present invention generally relates to a control apparatus for an electronic control type throttle of an internal combustion engine for e.g. a motor vehicle. More particularly, the present invention is concerned with a throttle control apparatus for an internal combustion engine which apparatus can detect the opening degree of a throttle valve with an enhanced accuracy by using an inexpensive A/D converter of a relatively low resolution. At this juncture, with the phrase xe2x80x9celectronic control type throttlexe2x80x9d, it is intended to mean a combination of a throttle valve disposed in an intake pipe of the internal combustion engine and an actuator therefor which is constituted by an electric motor.
2. Description of Related Art
In general, the throttle control apparatus of the internal combustion engine is designed to control the opening degree of the throttle valve so that it coincides with a desired or target opening degree which is arithmetically determined properly in dependence on the operation state of the motor vehicle. For further particulars, reference should be made to, for example, Japanese Patent Application Laid-Open Publication No. 222205/1998 (JP-A-10-222205).
The throttle control apparatus for the internal combustion engine includes a control means which is constituted by an ECU (Electronic Control Unit) for performing A/D conversion (analogue-to-digital conversion) of an output voltage of a throttle opening degree sensor for thereby arithmetically determining the target throttle opening degree on the basis of the value resulting from the A/D conversion. The electronic control type throttle is then so controlled that the opening degree thereof coincides with the determined target value through a feedback control.
In particular, in the idle operation mode of the engine, it is required to control the quantity of intake air flowing into the engine with a high accuracy in order to maintain a relatively low idle speed. To this end, the throttle control assuring a high reliability is demanded.
For realizing the high-accuracy control of the intake air flowing into the engine, the electronic control type throttle has to be controlled with a high accuracy, for which the capability of detecting the output voltage value of the throttle opening degree sensor with a high accuracy is prerequisite.
In this conjunction, a method of detecting accurately the sensor voltage indicative of the throttle opening degree (i.e., opening degree of the throttle valve) in an idle speed region of the engine is disclosed in Japanese Patent Application Laid-Open Publication No. 263703/1993 (JP-A-5-263703). According to this known method, two different throttle opening degree indicating voltages are detected, wherein the detected voltages for use are changed over between the idle speed region and the non-idle speed region.
However, the method disclosed in the publication cited just above suffers a problem that significant difference in level may undesirably make appearance between the detection values of the throttle opening degree upon changeover of the detection values although it depends on the accuracy of the changeover circuit as employed, which may exert adverse influence to the throttle control.
For coping with the problems mentioned above, it may be conceived to detect the throttle opening degree indicating voltage with a high accuracy by using the A/D converter exhibiting a high resolution, which is, however, very expensive, involving increased manufacturing cost of the control apparatus as a whole, giving rise to another problem.
As is apparent from the above, the conventional throttle control apparatus for the internal combustion engine, e.g. the apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 263703/1993 suffers a problem but significant difference in level may unwontedly make appearance between the detection values upon changeover thereof in dependence on the engine operation mode, which will exert unfavorable influence to the throttle control.
On the other hand, employment of the A/D converter exhibiting a high resolution for detecting the throttle opening degree voltage with high accuracy incurs increasing in the cost of the apparatus as a whole.
In the light of the state of the art briefed above, it is an object of the present invention to provide a throttle control apparatus for an internal combustion engine which apparatus is capable of controlling the throttle opening degree on the basis of the throttle opening degree indicating voltage which is detected with high accuracy by employing an inexpensive A/D converter of a relatively low resolution without resorting to the method of changing over the detection values of the throttle opening degree.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention a throttle control apparatus for an internal combustion engine, which apparatus includes an electronic control type throttle for controlling operation of the internal combustion engine, a throttle opening degree detecting means for detecting an opening degree of the electronic control type throttle, and a control means for controlling the opening degree of the electronic control type throttle to a target value in dependence on operation state of the internal combustion engine. The throttle opening degree detecting means includes a throttle opening degree sensor for generating a sensor voltage corresponding to or indicative of the opening degree of the electronic control type throttle, an offset means for transforming the sensor voltage into a plurality of offset-weighted voltages, an A/D converter for performing A/D conversion (analogue-to-digital conversion) of the plurality of offset-weighted voltages, and an adder means for executing processing of adding the plurality of offset-weighted voltages resulting from the A/D conversion, wherein a sum value resulting from the addition of the plurality of offset-weighted voltages undergone the A/D conversion is detected as the opening degree of the electronic control type throttle destined to be controlled.
By virtue of the arrangement of the throttle control apparatus for the internal combustion engine, it is possible to control the throttle opening degree on the basis of the throttle opening degree indicating voltage detected with high accuracy by employing an inexpensive A/D converter of relatively low resolution without resorting to the method of changing over the detection values of the throttle opening degree known heretofore.
In a mode for carrying out the invention, the offset means mentioned above should preferably be composed of impedance elements with the throttle opening degree detecting means preferably including a buffer inserted between the throttle opening degree sensor and the impedance elements, wherein a circuitry including the throttle opening degree sensor and a circuitry including the impedance elements should preferably be isolated from each other by means of the buffer.
With the arrangement described above, impedance of the offset means can be lowered, whereby the throttle control apparatus ensuring further enhanced accuracy for the A/D conversion can be implemented.
In another mode for carrying out the invention, the adder means mentioned above should preferably include an averaging means for performing average processing of the plurality of offset-weighted voltages undergone the A/D conversion, wherein a sum value resulting from the addition of the plurality of offset-weighted voltages averaged by the averaging means is detected as the opening degree of the electronic control type throttle destined to be controlled.
Owing to the arrangement described above, erroneous detection attributable to various sorts of noise can be evaded, whereby the throttle control apparatus ensuring the control performance of further enhanced accuracy can be implemented.
In yet another mode for carrying out the invention, the offset means mentioned above should preferably be composed of a plurality of resistors having impedance values differing from one another, wherein the A/D converter should preferably be provided with a plurality of input terminals and designed to fetch simultaneously the plurality of offset-weighted voltages inputted from terminals of the plural resistors through the plurality of input terminals.
With the arrangement described above, the time taken for executing the A/D conversion of the offset-weighted voltages can be reduced.
In still another mode for carrying out the invention, the offset means mentioned above should preferably be composed of a plurality of resistors having impedance values differing from one another, and a plurality of switching means for selectively validating the plurality of resistors. In that case, the throttle opening degree detecting means should preferably include a switching control means for performing on/off-control of the plurality of switching means in accordance with a predetermined sequence. On the other hand, the A/D converter mentioned above should preferably be provided with a single input terminal and designed to fetch time-serially the plurality of offset-weighted voltages delivered in response to validations of the resistors, respectively, by way of the single input terminal.
With the arrangement described above, the number of the input terminals of the A/D converter as employed for generating the offset-weighted voltages can be decreased, whereby other available terminals of the A/D converter can be used for effectuating other control(s).
In a further mode for carrying out the invention, the A/D converter mentioned above should preferably be so designed as to perform twice the A/D conversion processing for the plurality of offset-weighted voltages so that a value resulting from the second A/D conversion is inputted to the adder means.
With the arrangement described above, erroneous detection attributable to crosstalk in the A/D converter can be avoided, whereby the control accuracy can further be enhanced.
In a yet further mode for carrying out the invention, the A/D converter mentioned above should preferably be so designed as to execute the A/D conversion processing for the plurality of offset-weighted voltages in an ascending order, starting from the voltage of a minimum value.
With the arrangement described above, erroneous detection attributable to the crosstalk which may take place internally of the A/D converter can be avoided, whereby the control accuracy can further be enhanced.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.